On Schistosoma curassoni, S. haematobium and S. bovis from Senegal: development in Mesocricetus auratus, compatibility with species of Bulinus and their enzymes
TL;DR: A comparative study on the development of Senegalese isolates of Schistosoma curassoni, S. haematobium and S. bovis in hamsters is reported, together with the compatibility of these parasites with Bulinus spp.
Abstract: A comparative study on the development of Senegalese isolates of Schistosoma curassoni, S. haematobium and S. bovis in hamsters is reported, together with the compatibility of these parasites with Bulinus spp. and enzymes of adult worms. The mean worm return from 35 hamsters exposed to 100 cercariae each of S. curassoni was 11·5%, and of these 54% were paired, the remainder were single males. The growth and maturation of the worms were recorded from 40 to 100 days. The cross-over point (when paired females are of the same length as paired males) was reached at 42 days post-infection when the worms averaged 13·7 mm in length. The majority of tissue eggs (84·5%) were recovered from the liver, compared with 11% in the colon, 2·5% in the caecum and 1·6% in the small intestine. Estimates of the fecundity of paired females averaged 167 eggs/day per female worm. Snail-infection experiments showed S. curassoni to be compatible with B. umbilicatus, marginally compatible with B. senegalensis and incompatible with B...
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TL;DR: These data provide indisputable evidence for: the high occurrence of bidirectional hybridization between these Schistosoma species; the first conclusive evidence for the natural hybridisation between S. haematobium and S. curassoni; and demonstrate that the transmission of the different species and their hybrids appears focal.
Abstract: Background
Schistosomes are dioecious parasitic flatworms, which live in the vasculature of their mammalian definitive hosts. They are the causative agent of schistosomiasis, a disease of considerable medical and veterinary importance in tropical and subtropical regions. Schistosomes undergo a sexual reproductive stage within their mammalian host enabling interactions between different species, which may result in hybridization if the species involved are phylogenetically close. In Senegal, three closely related species in the Schistosoma haematobium group are endemic: S. haematobium, which causes urogenital schistosomiasis in humans, and S. bovis and S. curassoni, which cause intestinal schistosomiasis in cows, sheep and goats.
159 citations
Cites background from "On Schistosoma curassoni, S. haemat..."
...curassoni [55–56], hybridization between different Schistosoma species have been reported to affect the success of drug treatment in cattle [57], cause severe disease outbreaks and competitive exclusion of one species by the other [35–37] and laboratory hybrids have been observed to acquire enhanced characteristics such as infectivity, fecundity and growth rates [19,20,54]....
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TL;DR: Future studies will monitor the spread of human urinary and mesenteric schistosomiasis in the SRB, evaluate further the presence of praziquantel resistance/tolerance in S. mansoni, examine the heavily infected human population for pathological symptoms and determine the most appropriate methods to control this severe outbreak of human schistOSomiasis.
Abstract: Ecological changes in the Senegal River Basin (SRB) resulting from the construction of a barrage at Diama, Senegal on the Senegal River to prevent the intrusion of sea water into the river, and a dam at Manantali, Mali on the Bafing River to control the flow of water and to generate electricity, have been responsible for changes in the epidemiology of human schistosomiasis. The introduction of Schistosoma mansoni into the Lower and Middle Valleys of the SRB and subsequent spread of the parasite in the human population is recorded with regard to prevalence and intensity. New foci of S. haematobium are described. The reduction in salinity and change from an acidic to an alkaline environment in the water are beneficial to both the fecundity and growth of freshwater snails and transmission of the parasite. The creation of new irrigation canals and expansion of the rice fields have provided new habitats for intermediate hosts to colonize. The evidence for praziquantel resistance/tolerance by populations of S. mansoni and the possibilities of the development, production and testing of a vaccine against human schistosomiasis are discussed. Future studies will monitor the spread of human urinary and mesenteric schistosomiasis in the SRB, will evaluate further the presence of praziquantel resistance/tolerance in S. mansoni, will examine the heavily infected human population for pathological symptoms and determine the most appropriate methods to control this severe outbreak of human schistosomiasis.
123 citations
TL;DR: How early phenotypic identification and recent confirmation through molecular studies on naturally occurring infections, combined with experimental manipulations, have revealed evidence of viable hybridization and introgressions within and between human and animal schistosome species is reviewed.
Abstract: Hybridization of parasites is an emerging public health concern in our changing world. Hybridization and introgression in parasites and pathogens can have major impacts on the host and the epidemiology and evolution of disease. Schistosomiasis is a Neglected Tropical Disease of profound medical and veterinary importance across many parts of the world, with the greatest human burden within sub-Saharan Africa. Here we review how early phenotypic identification and recent confirmation through molecular studies on naturally occurring infections, combined with experimental manipulations, have revealed evidence of viable hybridization and introgressions within and between human and animal schistosome species. Environmental and anthropogenic changes in selective pressures following, for instance, new dam constructions, altered agricultural practices, together with mass drug administration programmes, may all be predicted to further impact the availability of suitable definitive and intermediate hosts for schistosomes. It is therefore imperative to understand the distribution and role of such novel zoonotic hybrid schistosomes on host range, drug efficacy, and hence ultimately transmission potential, if we are to achieve and maintain sustainable control.
112 citations
TL;DR: In this article, the authors conducted a study to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes.
Abstract: Extensive water development has taken place in the north of Senegal over the last decade, resulting in a large increase in the amount of fresh water for irrigation. The objectives of the present study were to determine the prevalence and intensity of Schistosoma mansoni and S. haematobium in the Senegal river basin (SRB), and to ascertain the distribution of the snail species acting as intermediate hosts for both species of schistosomes. The schistosomiasis survey started in January 1994 and was completed in March 1995. Compared to studies before the construction of the Diama dam, there was a significant increase in both the prevalence and intensity of urinary and intestinal schistosomiasis in the human population in parts of the SRB. From the 9014 people who were registered from 180 villages and 4 towns (10 districts), 7750 were examined. S. mansoni was found in the lower valley (lower delta-Senegal river, lower delta-Lampsar river, upper delta, and diere ) but not in the middle valley. The mean prevalence ranged from 4.4% in the lower delta-Senegal River to 71.8% in the zone of Lac de Guiers, where prevalence and intensity of infection were higher on the eastern side of the lake (81.3% with a mean number of 2088 eggs/g of faeces) compared with the western side (50.3% with a mean 1111 eggs/g). S. haematobium was recorded throughout the area of study, ranging from a mean prevalence of 0.37% in diere (lower valley) to 41.5% in the lower valley (Lampsar river), where the mean egg count was 313/10 mL of urine. Physical and chemical changes to the environment have favoured the spread and increase in the populations of freshwater snails. The only snail involved in the transmission of S. mansoni was Biomphalaria pfeifferi . Five species of bulinid snails were present— Bulinus globosus, Bu. umbilicatus, Bu. senegalensis, Bu. forskalii and Bu. truncatus —but only the first 3 species were involved in the transmission of S. haematobium in the lower and middle valleys.
108 citations
TL;DR: Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.
Abstract: Within each of the four species groups of Bulinus there are species that act as intermediate hosts for one or more of the seven species of schistosomes in the Schistosoma haematobium group, which includes the important human pathogens S. haematobium and S. intercalatum. Bulinus species have an extensive distribution throughout much of Africa and some surrounding islands including Madagascar, parts of the Middle East and the Mediterranean region. Considerable variation in intermediate host specificity can be found and differences in compatibility between snail and parasite can be observed over small geographical areas. Molecular studies for detection of genetic variation and the discrimination of Bulinus species are reviewed and two novel assays, allele-specific amplification (ASA) and SNaPshot™, are introduced and shown to be of value for detecting nucleotide changes in characterized genes such as cytochrome oxidase 1. The value and complexity of compatibility studies is illustrated by case studies of S. haematobium transmission. In Senegal, where B. globosus, B. umbilicatus, B. truncatus and B. senegalensis may act as intermediate hosts, distinct differences have been observed in the infectivity of different isolates of S. haematobium. In Zanzibar, molecular characterization studies to discriminate between B. globosus and B. nasutus have been essential to elucidate the roles of snails in transmission. B. globosus is an intermediate host on Unguja and Pemba. Further studies are required to establish the intermediate hosts in the coastal areas of East Africa. Biological factors central to the transmission of schistosomes, including cercarial emergence rhythms and interactions with other parasites and abiotic factors including temperature, rainfall, water velocity, desiccation and salinity are shown to impact on the intermediate host-parasite relationship.
83 citations
References
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Book•
01 Jan 1980
TL;DR: The biology of bulinus snail control local snail faunas chemical and physical factors life cycles and populations regions, lakes and rivers - biography.
Abstract: The first half of this book is primarily a systematic survey of the snails, beginning with glossaries, keys for identification to genera and a checklist of species. This is followed by a synopsis of species, with brief notes on ecology, distribution and parasites. Relationships are then described between snails and schistosomes and with other paras
1,076 citations
TL;DR: Comparisons between species suggest that exceptionally low rates of cercariaeProduction in the intermediate host may be compensated for by rapid rates of egg production in the definitive host, implying a degree of integration in the schistosome life-cycle not previously appreciated.
Abstract: Available data in the literature pertaining to the life-history characteristics of all known species of mammalian schistosomes have been gathered, and correlations between such variables as length of pre-patent period, adult worm size, rate of progeny production and progeny size have been explored. Accommodation of the schistosome life-cycle to the constraints imposed by certain host characteristics such as life-expectancy and size is discussed. Of the 23 known species of mammalian schistosomes, 20 species apparently rely to a major extent on relatively large-bodied and long-lived mammals such as primates, ungulates and proboscideans for their transmission. Only 1 species, Schistosomatium douthitti, is exclusively dependent on rodents for its transmission. S. douthitti attains maturity within its definitive host faster than any other mammalian schistosome, and is the only species known to be capable of producing viable eggs by facultative parthenogenesis. For all species of mammalian schistosomes, adult worm size, as estimated by female length, is positively correlated with the number of uterine eggs contained within the female (r = 0·682). For the 7 species for which data exist, rate of egg production/worm pair/day is positively correlated with uterine egg counts (r = 0·873) and inversely correlated with egg length (r = −0·787) and miracidium length (r = −0·953). Length of the pre-patent period is positively correlated with egg length (r = 0·503). With respect to the molluscan host, the number of cercariae produced by snails is positively correlated with the shell size of the snail (r = 0·657). For the 5 species for which data exist, the rate of egg production is inversely correlated with shell size of the intermediate host (r = −0·955) and the common logarithm of the number of cercariae produced (r = −0·893). Comparisons between species suggest that exceptionally low rates of cercariae production in the intermediate host may be compensated for by rapid rates of egg production in the definitive host, implying a degree of integration in the schistosome life-cycle not previously appreciated. Most species of mammalian schistosomes have long-lived definitive hosts, and snail hosts capable of producing many cercariae; compensatory relationships are therefore less obvious in such species. Additional quantitative data on all aspects of schistosome life-histories, particularly rate and duration of egg production, are needed to confirm or refute the relationships discussed above.
153 citations
TL;DR: The results of enzyme analyses of parasites isolated from human infections in the Transvaal show that hybridization does occur naturally in man and that the shape of the eggs produced is not necessarily a guide to the genetic constitution of the enclosed larvae.
Abstract: Some biological features of F1 hybrids between South African strains of Schistosoma haematobium and S. mattheei are described and compared with those of both parental species. The distinctive patterns of the G6PD and PGM isoenzymes, resolved by isoelectric focusing, of both species and of the hybrid are defined and the results of enzyme analyses of parasites isolated from human infections in the Transvaal are reported. These show that hybridization does occur naturally in man and that the shape of the eggs produced is not necessarily a guide to the genetic constitution of the enclosed larvae. The experimentally produced F1 hybrids exhibit heterosis in their increased infectivity to both snails and hamsters, in their more rapid growth and earlier maturation and in the increased daily egg production per female worm when compared with both of the parental species. The possible practical implications of this are discussed.
93 citations
89 citations